Conventionally, a resin plate member is put to various uses (e.g., a floor material of a trunk of an automobile or the like). In general, the resin plate member is cut into a desired shape corresponding to its use, and is then subject to a step of performing various working processes on its end portion (terminal portion) including a cut surface from the viewpoint of improving beauty of the resin plate member and reducing a sense of harm, whereby the resin plate member is manufactured.
For example, in one of conventional working methods (hereinafter referred to as “a conventional method”), a notch having a specific shape is formed in a pressed surface while an end portion of a plate member formed of a synthetic resin is heated and pressed, the end portion of the plate member is bent (folded) along the notch, and a cut surface of the end portion is thereby accommodated inside the plate member. With this, the conventional method prevents the cut surface from being exposed at the end portion of the plate member and enhances the beauty of the plate member and the like (see, e.g., Patent Document 1).    Patent Document 1: Japanese Patent Application Publication No. 2000-190384